1. Field of the Invention
The present invention relates to calibration of a radar antenna and the associated software, and particularly to calibrating such an antenna and software in a missile in flight, or just prior to flight.
2. Description of the Related Art
Missiles that use radar as part of their guidance systems generally have a radar antenna in the nose of the missile behind a radome. The radome includes a conical cap which is made of a radar-opaque material, typically metal. The balance of the radome forward of the radar antenna and behind the cap is made of a material transparent to radar, such as a suitable ceramic material.
The radar antenna is calibrated in the course of manufacture and initial setup. Due to manufacturing repeatability it is very difficult to have exactly the same characteristics inside each radome—for example, there may be fluctuations in radome thickness and variations in antenna installations within radome. Typically calibration is done in an anechoic chamber with a source of microwave radiation of known energy.
Calibration of a radar antenna may be critical to its proper performance. This is especially true where sophisticated and sensitive software is used to interpret the received signals. For example, software used to distinguish the intended target from various decoys, jamming and/or camouflaging defensive measures associated with the target works better after calibration. Even if accurately calibrated during initial manufacture, the antenna's response to incoming signals can vary over time. For example, after storage of the missile for a long period of time, the antenna can suffer slight physical changes which alter its response. In addition, the very act of launching a missile may subject it to forces and/or temperatures which alter its response.
Because the radar antenna's response can change over time, there is a need for a system and apparatus that can be used to recalibrate a radar antenna in a missile while the missile is in flight, or shortly before flight.